The present invention relates generally to capacitors and relates more particularly to electrochemical-electrolytic capacitors.
Capacitors are devices that store electrical charge. Capacitors typically include a pair of electrically conductive electrodes insulated from one another by a dielectric.
One type of capacitor is an electrochemical capacitor, an example of which is disclosed in U.S. Pat. No. 5,136,474, inventors Sarangapani et al., which issued Aug. 4, 1992, and which is incorporated herein by reference. The electrochemical capacitor of the aforementioned patent includes a proton-conducting dielectric in the form of a solid ionomer membrane. Said solid ionomer membrane is said to be preferably a perfluorocarbon sulfonic acid polymer, such as that formed by the copolymerization of polytetrafluoroethylene and a polyfluorovinyl ether containing pendant sulfonic acid groups. A first electrode is bonded to and is in intimate contact with a first surface of the solid ionomer membrane, and a second electrode is bonded to and is in intimate contact with a second surface of the solid ionomer membrane. Each of the first electrode and the second electrode is made up of RuOx (wherein x is approximately 2) particles that have been coated with a quantity of the solid ionomer, the ionomer-coated RuOx particles of each electrode being in intimate contact with one another in such a way that proton conductivity within each electrode is afforded by the ionomer coating and electron conductivity within each electrode is afforded by the RuOx particles. Because ionomer is continuously present in the first and second electrodes and in the dielectric, a continuous proton transport path exists between the two electrodes. On the other hand, a continuous electron transport path does not exist between the two electrode due to the presence of the dielectric; consequently, electrical charge is stored in the electrodes. The electrochemical capacitor also includes a pair of current collectors, one of the current collectors being bonded to the outside surface of the first electrode and in intimate contact with RuOx particles therein for electron conductivity therewith, the other current collector being bonded to the outside surface of the second electrode and in intimate contact with RuOx particles therein for electron conductivity therewith.
Another type of capacitor is an electrochemical-electrolytic capacitor, an example of which is disclosed in U.S. Pat. No. 5,369,547, inventor Evans, which issued Nov. 29, 1994, and which is incorporated herein by reference. The electrochemical-electrolytic capacitor of the aforementioned patent includes a metal container that functions as the cathode of the capacitor, the metal container having an inside surface and an outside surface. A porous coating including an oxide of a metal, which metal is selected from the group consisting of ruthenium, iridium, nickel, rhodium, platinum, palladium, and osmium, is formed on the inside surface of the metal container. Instead of forming the porous coating directly on the metal container, the porous coating may be formed on a metal foil disposed within the container and welded to the inside surface of the container. An anode, which is selected from the group consisting of tantalum, aluminum, niobium, zirconium, and titanium, is disposed within the container and is spaced from the porous coating by electrically insulating spacers. The anode is said to be preferably a conventional sintered porous tantalum anode of the type used in conventional wet slug tantalum capacitors. A liquid electrolyte, which is said to be most typically a sulfuric acid solution, is disposed within the container in contact with the porous coating and the anode.
Another example of an electrochemical-electrolytic capacitor is disclosed in U.S. Pat. No. 5,559,667, inventor Evans, which issued Sep. 24, 1996, and which is incorporated herein by reference. The electrochemical-electrolytic capacitor of the aforementioned patent is nearly identical to the electrochemical-electrolytic capacitor of the above-discussed U.S. Pat. No. 5,369,547, the only difference between the two capacitors being that, in the capacitor of U.S. Pat. No. 5,559,667, the liquid electrolyte of U.S. Pat. No. 5,369,547 is replaced with a solid electrolyte that is positioned between the porous coating and the anode. Materials said to be usable as the solid electrolyte are polypyrrole, NAFION® perfluorosulfonic acid (PFSA) polymer and polyaniline, as well as semi-solids, such as an aqueous electrolyte solution with silica added to form a gel.
Other publications relating to electrochemical-electrolytic capacitors include Evans, “The Littlest Big Capacitor—An Evans Hybrid,” Proceedings of The Fifth International Seminar on Double Layer Capacitors and Similar Energy Storage Devices, Deerfield Beach, Fla. (1995) and Evans, “170 Volt Tantalum Hybrid Capacitor—Engineering Considerations,” Proceedings of The Seventh International Seminar on Double Layer Capacitors and Similar Energy Storage Devices, Deerfield Beach, Fla. (1997), both of which are incorporated herein by reference.